Duet 3 Bed Auto-Compensation Producing Invisible Z Offset

Video describing the issue from forum post forum.duet3d.c...
I appear to be getting an invisible offset addition whenever I use a Bed Compenstation Feature, either G30 S3 or G29 that cannot be homed out

[@akro9777]

i think you mistaken Z trigger height for Z offset in G31 X-22 Y60 Z1.6 P25 ;XY offsets Z trigger height. Reset trigger height to 0 prior with M851 Z0 and m500, and then run G31 X-22 Y60 Z1.6 P25 (whaterver yours is). This problem use to drive me nuts because i know what my Z offset is, but G31 only cares bout trigger height. which is how far above bed nozzle is when probe triggers. Z offset would be how far the probe is from nozzle. hope this helps, if not please ignore.

[@AlexPerez-dv3js]

Nice job in cleaning up the wiring and overall a good looking printer. Will be installing my duet 3 board soon.

[@lauckstreet]

I think the problem you're having has to do with the existing z offset being stored in the eprom. You must first erase the existing z offset and set it to 0 before you run the bed compensation feature. Try sending the M851 Z0 command to the Duet first, then M500 to store the z=0 offset. Send a M501 to set active parameters and then M503 to view them to verify that the z offset is now zero. Perform your bed compensation. When through z should be at the correct height. Send M501 and then M503 again to verify what the z offset now is. I ran into a similar problem with my Ender 5 Plus.

[@LukesLaboratory]

Since I made this video, I switched to an inductive probe (I got a spring steel surface so I could use it) and without any other changes (I switched config for the probe # but that's it) the problem went away. Seems related to the bltouch +rrf3+rpi. It can now easily run levelling without concern. Thanks for posting

[@lauckstreet]

@@LukesLaboratory Good to know. I just put a Duet 2 Maestro into my Ender 5 Plus and have had problems with the autoleveling feature myself, but I did discover yesterday that the Ender 5 Plus has a different leadscrew on the Z axis. The Ender 5 uses 400 steps per mm on the Z axis but the Ender 5 Plus uses 800. This might be why I've been having trouble with the autoleveling on that machine. I corrected the steps and it's printing perfectly now but I haven't tried the autoleveling since I changed the steps per mm on the Z axis. I'll give it a try today. The problem I've been having has to do with the Z offset but now I understand why since the steps per mm on the Z axis was only half of what it should have been.

[@HDFoxra]

I had this exact issue. I can't remember what I did to fix it though. But I remember it had something to do with it keeping an offset stored somewhere. It was a stupid simple fix when i found it out though. but yea, check your config files... and then make sure your eeprom doesn't have it stored as well.

[@LukesLaboratory]

Thanks for the reply! I had resolved this one a while ago as i switched to my TC carriage and started using just a regular mechanical switch.

[@explosiveenterprises1479]

Ever figure this out?

[@LukesLaboratory]

No - firmware upgrades have not addressed my issues yet.

[@MichaelHaertel]

What printer is this? I ordered an Sk-Go but looks like it will be delayed because of issues in China so thinking about building another CoreXY with Duet 3 and 3 point leveling.

[@LukesLaboratory]

Hi! This is my upcoming stablebot, a large, scalable toolchanging 3d printer!

[@ralmslb]

@@LukesLaboratory looks great. I will be converting my CR10 into a CoreXY printer. Would love to see more about your printer.

[@psybluette]

What is your small display? Looks great. Is it paneldue? or small monitor? I want to get it.

[@LukesLaboratory]

amzn.to/2URW1tF

[@psybluette]

@@LukesLaboratory much thanks for kink reply. Good luck.

[@SteamLabs]

I know this is old, but I ran across the solution. duet3d.dozuki.com/Wiki/Bed_levelling_using_multiple_independent_Z_motors#Section_Prerequisites "If your bed is not perfectly flat or the gantry sags a little when the head is over the middle of the bed, the process will cause a small shift in the Z=0 position. To correct this, if you are using the Z probe to do Z homing, you can just re-home Z at the end of your bed.g file." Hope it helps.

[@LukesLaboratory]

Hi There! As I showed in the video (which is why this video has no cuts, I wanted to show complete continuity) After using bed tramming, i *completely* re-homed the machine. That is, I homed EVERYTHING from scratch after tramming. That means that all offsets from G32 should be wiped as it re-sensed the bed at its new flat plane. Start the video at 2:52, where i show that even though I trammed the bed, and then completely re-homed it (that is, re-sensed its bed location) there is something that was stuck in firmware causing the issue. The machine no longer has an issue as future firmware removed the bug, without me changing anything but updates and swapping to an inductive probe. Must have been in the BLTouch code